Oil capture scoop

ABSTRACT

A plurality of circumferentially spaced apart oil scoops are designed to capture oil being slung from an inner shaft across an annulus to an outer shaft which rotates in a direction opposite to the inner shaft. The scoops rotate with and are a part of the outer shaft assembly. The scoops, in one embodiment, are defined by opposed spaced apart wall surfaces oriented substantially parallel to the relative velocity vector of the jets of oil as they travel outwardly from the inner shaft across the annulus. Splashing of the oil as it is picked up by the scoops is minimized by this invention.

The Government has rights in this invention pursuant to Contract No.F33657-79-C-0730 awarded by the Department of the Air Force.

DESCRIPTION CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application is of related subject matter to commonly owned U.S Pat.application Ser. No. 490,699, now U.S Pat. No. 4,453,784, herewithtitled "Means For Feeding Oil Between Counterrotating Shafts" by RobertJ. Kildea, Jorge A. Alcorta and Brian Richardson.

TECHNICAL FIELD

This invention relates to intershaft bearings and means for providingoil thereto.

BACKGROUND ART

Twin spool gas turbine engines and other kinds of rotating machinery mayinclude concentric shafts which rotate at different speeds or inopposite directions. In some cases one shaft may be supported from theother through a bearing. It is typical of the prior art to bring oil tothe inner race of a bearing through passageways in the shaft to whichthe inner race is attached. If the bearing is external of the outershaft, and if the oil supply for the bearing comes from within the innershaft, the oil must be brought across the annulus between the inner andouter shaft and thence to the inner race of the bearing. Depending uponthe bearing and shaft arrangement and the relative axial velocity of oneshaft to the other, certain problems may arise in transferring the oilfrom the inner shaft radially across the annulus to the outer shaft. Forexample, due to large centrifugal forces, it is difficult to prevent theoil from splashing as it strikes the outer shaft after flowing acrossthe annulus. Splashing produces an oil mist within the annulus which canbe swept away by air flow through the annulus. Over a period of time theloss of oil may be significant. If temperatures, temperature gradientsand the relative angular velocities of the shafts permit, annularintershaft seals may be disposed on either side of the oil streamflowing across the annulus to prevent loss of the oil mist. Close sealsmay not be possible in situations where high temperatures, large thermalgradients, and high relative angular velocities are present. It is tothese latter problems that the present invention is directed.

Commonly owned U.S. Pat. No. 3,756,672 is directed to damping shaftvibrations of two concentric rotating shafts wherein one shaft issupported from the other shaft by means of a bearing disposedtherebetween. Several bearing and shaft arrangements are shown. None ofthem appear to have the problems which the present invention is intendedto solve.

DISCLOSURE OF INVENTION

One object of the present invention is to enable oil to be brought fromwithin one shaft to a concentric surrounding shaft across an annular gaptherebetween with a minimum of splashing, even if one shaft has a highangular velocity relative to the other shaft.

In accordance with the present invention, a shaft assembly comprises aninner shaft, an outer shaft surrounding and spaced from the inner shaftand adapted to rotate counter to the inner shaft and defining an axiallyextending annulus therebetween, a plurality of circumferentiallydisposed recesses in the inside surface of the outer shaft substantiallyaligned with the outlets of oil carrying passageways through the innershaft for receiving oil from the passageways, and passage means in fluidcommunication with the recesses for carrying oil therefrom through theouter shaft. In a preferred embodiment the recesses in the outer shaftwhich capture the oil from the oil compartments are in the form of aplurality of circumferentially, closely spaced apart scoops havingopposed spaced apart wall surfaces which are oriented substantiallyparallel to the relative velocity vector of the jets of oil as theytravel from the inner shaft across the annulus, thereby reducingsplashing of the oil as it enters the recesses.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in the light of the followingdetailed description of preferred embodiments thereof as shown in theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a simplified cross-sectional view of the rear bearingcompartment portion of a dual spool gas turbine engine.

FIG. 2 is a sectional view taken along the line 2--2 of FIG. 1.

FIG. 3 is a view taken along the line 3--3 of FIG. 1.

FIG. 4 is a view similar to FIG. 2 showing an alternate embodiment ofthe invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As an exemplary embodiment of the present invention consider the portionof a twin spool gas turbine engine shown in FIG. 1, which has beensimplified for clarity. More specifically, what is shown in FIG. 1 isthe rearward end portion of the low spool 10, the rearward end portionof the high spool 12, and a portion of nonrotating, fixed supportstructure 14. The low and high spools 10, 12 rotate counter to eachother about the engine axis 15.

The low spool 10 comprises a main, hollow, inner shaft 16, a hub 18, aturbine wheel 20, a spline adapter 22, and a splined shaft 23 integralwith the hub 18. The spline adapter 22 is fixed relative to the innershaft 16 by means not shown. The hub 18 is also fixed relative to themain shaft 16 and rotates therewith through a spline connection 24between the shaft 23 and the spline adapter 22. The turbine wheel 20, inthis embodiment, is the last or furthest downstream stage of the lowspool 10 and is attached to the hub 18 by means of bolts 26 and nuts 28.The low spool 10 also includes an outer bearing support shaft 30concentric with the main shaft 16, integral with the hub 18, andextending axially upstream from the hub 18.

The portion of the high spool 12 shown in FIG. 1 comprises a shaftassembly 32 and a portion of a hub 34 integral with the shaft assembly32. A turbine wheel of the high spool is attached directly to the hub34, but is outside the view of FIG. 1. The shaft assembly 32 is disposedradially between the inner shaft 16 and outer shaft 30.

The low spool 10 is mounted for rotation with respect to the fixedsupport structure 14 and is supported by the structure 14 through afirst roller bearing 36 disposed radially outwardly of the splined shaft23 and downstream of the low spool hub 18. A ball bearing (not shown)supports the forward end of the low spool 10. The first bearing 36comprises an outer race 38, and inner race 40, and a plurality ofrolling elements 42 disposed therebetween. The outer race 38 is fixedlyattached to the support structure 14; and the inner race 40 is fixedlyattached to and rotates with the low spool 10. Oil is fed to the firstbearing 36 from within the main shaft 16 by means of a plurality ofradial holes 41 through, respectively, the main shaft 16 spline adapter22 and splined shaft 23, which holes are in fluid communication witheach other.

The aft end of the high spool 12 is supported or "hung" from the lowspool 10 through a second roller bearing 44 disposed between the highspool shaft assembly 32 and the low spool outer shaft 30. The secondbearing 44 includes an outer race 46, an inner race 48, and a pluralityof rolling elements 50 disposed therebetween in conventional fashion.The outer race 46 is fixedly attached to the outer shaft 30 and rotatestherewith; and the inner race 48 is fixedly attached to the shaftassembly 32 and rotates therewith.

The arrangement of shafts and bearings in this embodiment is sometimesreferred to as a "piggyback" arrangement since the loads imposed uponthe bearing 44, which directly supports the high spool 12, areultimately passed through the bearing 36 which directly supports the lowspool. It is this type of arrangement which sometimes requires, as inthe present embodiment, that the oil being fed into a bearing jumpacross an annulus between shafts which are rotating at different speedsand/or in opposite directions.

In accordance with the present invention, the low spool 10 includes asleeve 52 surrounding the main shaft 16 and radially spaced therefromdefining an axially extending annulus 54 therebetween. In thisembodiment the sleeve 52 is integral with and a part of the splineadapter 22, although it need not be. The sleeve 52 has a radiallyinwardly facing surface 56 and a radially outwardly facing surface 58.Extending radially inwardly from the inwardly facing surface 56 to anoutwardly facing surface 60 of the shaft 16 are a plurality of walls 62,each wall 62 defining a separate, axially elongated oil compartment 64(see, also, FIG. 3). The oil compartments 64 are found in number in thepresent instance, and are circumferentially and evenly spaced apart fromeach other. Each compartment 64 has associated with it an oil entrancepassageway 66 through the shaft 16 and an oil exit passageway 68 throughthe sleeve 52. The oil entrance passageway 66 has an outlet 70 and aninlet 72. The oil exit passageway 68 has an inlet 74 and an outlet 76.The outlet 70 is intentionally not aligned with the inlet 74.

The shaft assembly 32 includes a shaft end portion 78 and an annular oilscoop ring 80. The ring 80 fits tightly against the inside surface 82 ofthe shaft end portion 78. The ring 80 is spaced radially outwardly fromthe surface 58 of the sleeve 52 thereby defining a second annulus 85therebetween of varying radial width due to the uneveness of the ring'sinner surface 84. Within the surface 84 are a plurality ofcircumferentially spaced apart recesses 86 which are in substantiallythe same axial plane as the outlets 76 of the oil exit passageways 68.As used herein, the phrase "axial plane" is a plane perpendicular to theengine axis 15. In the present embodiment, and as best seen in FIG. 2,the recesses 86 are radially extending slots through the scoop ring 80.Each of the plurality of recesses 86 is in fluid communication with theinner race 48 of the bearing 44 by means of passageways 88 through theshaft assembly 32, which passageways are interconnected to each other bymeans of an annulus 123 in the shaft 78. A more detailed description ofthe recesses 86 is set forth below.

In operation, oil flows along the inside surface 90 of the main shaft 16and into the passageways 66, whereupon the radial and angular velocityof the oil increases due to the centrifugal forces created by therotating shaft. Since the outlets 70 of the oil entrance passageways 66and the inlets 74 to the oil exit passageways 68 are not radiallyaligned, the oil entering the compartments 64 from the passageways 66must travel in a substantially axial direction to reach the exitpassageway 68. Its radial velocity is thereby reduced to zero. Upontraveling through the exit passageways 68, a radial velocity is onceagain imparted to the oil. The velocity vector of the oil as it leavesthe outlets 76 of the passageways 68 is depicted by the velocity vector92 in FIG. 2. Note that the radial component of the velocity vector 92is small relative to the tangential velocity of the oil. This is due totwo features of the present invention: first, the hereinabove-mentionedreduction in the radial velocity to zero as the oil enters thecompartment 64; and, second, the short radial distance between theinlets 74 and the outlets 76 of the passageways 68 (i.e., there islittle distance or time to gain radial speed). The oil from the oil exitpassageways 68 travels across the second annulus 85 and enters therecesses 86 of the shaft assembly 32. The oil is fed from the recesses86 to the inner race 48 of the bearing 44 via the passageways 88.

The shape of the recesses 86 in this preferred embodiment is best shownin FIGS. 1 and 2. Each recess 86 comprises a bottom wall surface 94which faces radially inwardly; radially extending, axially spaced apart,opposed sidewall surfaces 96; and, first and second scoop surfaces 98,100, respectively. The scoop surfaces 98, 100 adjoin the opposingsidewall surfaces and are substantially parallel to each other. Thefirst scoop surface 98 faces radially inwardly, and the second scoopsurface 100 faces radially outwardly. Arrows 102, 103 indicate thedirection of rotation of the high and low spools 12, 10, respectively.The radially inwardly facing first scoop surface 98 of a recess 86 iscircumferentially spaced from the radially outwardly facing second scoopsurface 100 of that recess in the direction of rotation 102 of the shaftassembly 32. The radially inwardly facing first scoop surface 98 of onerecess 86 and the radially outwardly facing second scoop surface 100 ofthe next adjacent (in the direction of rotation 102) recess 86substantially intersect along a line 104 (FIG. 1) parallel to the axis15, thereby defining a wedge 106. In a cross section perpendicular tothe axis 15, the radially inwardly facing first scoop surface 98 formsan angle with a radial line (such as the line 108) passing through theintersection line 104, which angle is at least 90° and is substantiallyequal to or greater than the angle the velocity vector 92 makes with thesame line under normal operating conditions. The object is to minimize,if not eliminate, striking of the oil against the surface 98, whichwould cause the oil to splash toward the annulus 85. Oil striking thesurface 100 tend to splash radially outwardly toward the bottom surface94 of the recess, which is less of a problem.

Some splashing of the oil as it enters the recesses 86 may beunavoidable; and there may be a mist of oil within and above therecesses 86, which mist can move through the annulus 85 and be lost.Over a long period of time this loss can be significant, and it isdesirable to reduce the loss to a minimum. For this reason the ring 80includes an annular depression 110 immediately aft of the recesses 86,and a plurality of circumferentially spaced apart dishlike depressions87 immediately forward of the recesses 86. Passageways 114, 116 throughthe ring 80 provide fluid communication between the recesses 86 and,respectively, the annulus 110 and depressions 87 for returning therecaptured oil mist to the recesses 86, with the help of centrifugalforces. To further reduce the amount of oil lost to air flowing throughthe annulus 85 from the cavity 65 to the cavity 124, the ring 80includes baffles 126, 128, and 129 which reduce the radial dimension ofthe annulus 85 to a minimum in two axial planes causing most of the airto flow through holes 67 in the sleeve 52 into and through annulus 54(around compartments 64) away from the area of oil transfer acrossannulus 85.

An alternate embodiment for the construction of the recesses 86 is shownin FIG. 4. The only difference is that the outwardly facing scoopsurface 200 is curved rather than flat. Flat is preferable for ease ofmachining.

Although the invention has been shown and described with respect to apreferred embodiment thereof, it should be understood by those skilledin the art that other various changes and omissions in the form anddetail thereof may be made therein without departing from the spirit andthe scope of the invention.

We claim:
 1. A shaft assembly comprising:first hollow shaft meansrotatable about an axis and having an inner surface and an outwardlyfacing surface; second shaft means adapted to rotate about said axis ina direction counter to the direction of rotation of said first shaftmeans and including a shaft portion surrounding said first shaft means,said shaft portion having a radially inwardly facing surface spacedradially outwardly from said outwardly facing surface defining anaxially extending annulus therebetween, said shaft portion includingwall means defining a plurality of circumferentially and closely spacedapart recesses in said inwardly facing surface, each of said recessesincluding a radially inwardly facing bottom wall surface, radiallyextending, axially spaced apart, opposed side wall surfaces, and firstand second scoop surfaces adjoining said side wall surfaces, said firstscoop surface facing radially inwardly and said second scoop surfacefacing radially outwardly, said first scoop surface being spacedcircumferentially from said second scoop surface in the direction ofrotation of said outer shaft means, said first scoop surface of eachrecess and said second scoop surface of the recess adjacent theretosubstantially intersecting along a line parallel to said axis defining awedge; said inner shaft means having a plurality of oil passagewaysextending from said inner surface to said outwardly facing surface, saidoil passageways having outlets in the same axial plane as said recessesfor directing oil from said oil passageways, across said second annulus,into said recesses; and means defining second passageways through saidsecond shaft means in fluid communication with said recesses forcarrying oil from said recesses through said second shaft means.
 2. Theshaft assembly according to claim 1 wherein said first scoop surface isflat, and, in a cross section perpendicular to said axis, said firstscoop surface forms an angle with a radial line passing through saidintersection line of said first and second scoop surfaces, which angleis at least 90° and is selected to be substantially equal to or greaterthan the angle of the velocity vector of the oil from said passagewayoutlets under normal engine operating conditions.
 3. The shaft assemblyaccording to claim 2 wherein said second scoop surface is flat andparallel to said first scoop surface.
 4. A shaft assemblycomprising:first shaft means rotatable about an axis and includinghollow inner shaft means and an outer shaft portion spaced radiallyoutwardly from said inner shaft means, said inner shaft means having aninner surface and an outwardly facing surface; second shaft meansrotatable about said axis in a direction counter to the direction ofrotation of said first shaft means and including means defining a shaftend portion disposed radially between said inner shaft means and outershaft portion of said first shaft means and having a radially inwardlyfacing surface spaced radially outwardly from said inner shaft meansdefining an axially extending annulus therebetween, including wall meansdefining a plurality of circumferentially and closely spaced apartrecesses in said inwardly facing surface, each of said recessesincluding a radially inwardly facing bottom wall surface, radiallyextending, axially spaced apart, opposed side wall surfaces, and firstand second scoop surfaces adjoining said side wall surfaces, said firstscoop surface being flat and facing radially inwardly and said secondscoop surface facing radially outwardly, said first scoop surface beingspaced circumferentially from said second scoop surface in the directionof rotation of said outer shaft means, said first scoop surface of eachrecess and said second scoop surface of the recess adjacent theretosubstantially intersecting along a line parallel to said axis defining awedge, wherein, in a cross section perpendicular to said axis, saidfirst scoop surface forms an angle with a radial line passing throughsaid intersection line of said first and second scoop surfaces, whichangle is at least 90° and is selected to be substantially equal to orgreater than the angle of the velocity vector of the oil from saidpassageway outlets under normal engine operating conditions; firstbearing means disposed between said second shaft means end portion andsaid first shaft means outer shaft portion, said bearing meanscomprising inner race means, outer race means, and rolling elementsdisposed between said inner and outer race means, said outer race meansbeing attached to and fixed relative to said first shaft means outershaft portion, said inner race means being attached to and fixedrelative to said second shaft means end portion; said inner shaft meanshaving a plurality of oil passageways extending from said inner surfaceto said outwardly facing surface, said oil passageways having outlets inthe same axial plane as said recesses for directing oil from said oilpassageways, across said second annulus, into said recesses; and meansdefining second passageways in said second shaft means in fluidcommunication with said recesses for carrying oil from said recesses,through said second shaft means, to said first bearing means inner racemeans.